Loss of mitofusin 2 links beta-amyloid-mediated mitochondrial fragmentation and Cdk5-induced oxidative stress in neuron cells

Age-related accumulation of phosphorylated mitofusin 2 protein in retinal ganglion cells correlates with glaucoma progression

Dysregulation of axonal bioenergetics is likely a key mechanism in the initiation and progression of age-related neurodegenerative diseases. Glaucoma is a quintessential neurodegenerative disorder characterized by progressive deterioration of the optic nerve (ON) and eventual death of retinal ganglion cells (RGCs). Age and elevation of intraocular pressure are key risk factors in glaucoma, but the common early hallmarks of decreased axonal transport and increased bioenergetic vulnerability likely underlie disease initiation. We examined the correlation between bioenergetics and axonal transport with mitochondrial mutation frequency and post-translational modifications of mitofusin 2 (Mfn2) in RGCs during glaucoma progression. No increase in the frequency of mtDNA mutations was detected, but we observed significant shifts in mitochondrial protein species. Mfn2 is a fusion protein that functions in mitochondrial biogenesis, maintenance, and mitochondrial transport. We demonstrate that Mfn2 accumulates selectively in RGCs during glaucomatous degeneration, that two novel states of Mfn2 exist in retina and ON, and identify a phosphorylated form that selectively accumulates in RGCs, but is absent in ON. Phosphorylation of Mfn2 is correlated with higher ubiquitination, and failure of the protein to reach the ON. Together, these data suggest that post-translational modification of Mfn2 is associated with its dysregulation during a window of metabolic vulnerability that precedes glaucomatous degeneration. Future work to either manipulate expression of Mfn2 or to prevent its degradation could have therapeutic value in the treatment of neurodegenerative diseases where long-tract axons are vulnerable.

Upregulation of miR-195 accelerates oxidative stress-induced retinal endothelial cell injury by targeting mitofusin 2 in diabetic rats

This study was performed to investigate the oxidative stress-induced miRNA changes in relation to pathogenesis of diabetic retinopathy (DR) and to establish a functional link between miRNAs and oxidative stress-induced retinal endothelial cell injury. Our results demonstrated that oxidative stress could induce alterations of miRNA expression profile, including up-regulation of miR-195 in the diabetic retina or cultured HMRECs after exposed to H₂O₂ or HG (P < 0.05). Oxidative stress also resulted in a significant reduction of MFN2 expression in diabetic retina or HMRECs (P < 0.05). Overexpression of miR-195 reduced MFN2 protein levels, and induced tube formation and increased permeability of diabetic retinal vasculature. The luciferase reporter assay confirmed that miR-195 binds to the 3' -untranslated region (3'-UTR) of MFN2 mRNA. This study suggested that miR-195 played a critical role in oxidative stress-induced retinal endothelial cell injury by targeting MFN2 in diabetic rats.

Activation of mitophagy leads to decline in Mfn2 and loss of mitochondrial mass in Fuchs endothelial corneal dystrophy

Human corneal endothelial cells (HCEnCs) are terminally differentiated cells that have limited regenerative potential. The large numbers of mitochondria in HCEnCs are critical for pump and barrier function required for corneal hydration and transparency. Fuchs Endothelial Corneal Dystrophy (FECD) is a highly prevalent late-onset oxidative stress disorder characterized by progressive loss of HCEnCs. We previously reported increased mitochondrial fragmentation and reduced ATP and mtDNA copy number in FECD. Herein, carbonyl cyanide m-chlorophenyl hydrazone (CCCP)-induced mitochondrial depolarization decreased mitochondrial mass and Mfn2 levels, which were rescued with mitophagy blocker, bafilomycin, in FECD. Moreover, electron transport chain complex (I, V) decrease in FECD indicated deficient mitochondrial bioenergetics. Transmission electron microscopy of FECD tissues displayed an increased number of autophagic vacuoles containing degenerated and swollen mitochondria with cristolysis. An elevation of LC3-II and LAMP1 and downregulation of Mfn2 in mitochondrial fractions suggested that loss of fusion capacity targets fragmented mitochondria to the pre-autophagic pool and upregulates mitophagy. CCCP-induced mitochondrial fragmentation leads to Mfn2 and LC3 co-localization without activation of proteosome, suggesting a novel Mfn2 degradation pathway via mitophagy. These data indicate constitutive activation of mitophagy results in reduction of mitochondrial mass and abrogates cellular bioenergetics during degeneration of post-mitotic cells of ocular tissue.

Astragaloside IV rescues MPP+-induced mitochondrial dysfunction through upregulation of methionine sulfoxide reductase A

Methionine sulfoxide reductase (Msr) repairs oxidatively damaged proteins through acting as an antioxidant. Oxidative stress has been postulated to cause the mitochondrial dysfunction that is associated with aging and certain diseases, including Parkinson's disease (PD). The present study investigated the protective effects of astragaloside IV (AS-IV) on 1-methyl-4-phenylpyridinium (MPP⁺)-induced mitochondrial dysfunction through MsrA in PC12 cells. This revealed that oxidative stress reduced the expression of MsrA following MPP⁺ treatment. AS-IV was demonstrated to protect PC12 cells from MPP⁺-induced oxidative damage through upregulating MsrA. MsrA expression was dependent on the Sirt1-FOXO3a signaling pathway. In addition, knockdown of MsrA reduced the protective effects of AS-IV, indicating that the antioxidant effects of AS-UV occurred through MsrA. These results suggest that AS-IV exerts antioxidant effects and regulates mitochondrial function. Thus, AS-IV may serve as an effective therapeutic agent for aging and PD.

Linking deregulation of non-coding RNA to the core pathophysiology of Alzheimer's disease: An integrative review

The human genome encodes a vast repertoire of protein non-coding RNAs (ncRNA), some specific to the brain. MicroRNAs, which interfere with the translation of target mRNAs, are of particular interest since their deregulation has been implicated in neurodegenerative disorders like Alzheimer's disease (AD). However, it remains challenging to link the complex body of observations on miRNAs and AD into a coherent framework. Using extensive graphical support, this article discusses how a diverse panoply of miRNAs convergently and divergently impact (and are impacted by) core pathophysiological processes underlying AD: neuroinflammation and oxidative stress; aberrant generation of β-amyloid-42 (Aβ42); anomalies in the production, cleavage and post-translational marking of Tau; impaired clearance of Aβ42 and Tau; perturbation of axonal organisation; disruption of synaptic plasticity; endoplasmic reticulum stress and the unfolded protein response; mitochondrial dysfunction; aberrant induction of cell cycle re-entry; and apoptotic loss of neurons. Intriguingly, some classes of miRNA provoke these cellular anomalies, whereas others act in a counter-regulatory, protective mode. Moreover, changes in levels of certain species of miRNA are a consequence of the above-mentioned anomalies. In addition to miRNAs, circular RNAs, piRNAs, long non-coding RNAs and other types of ncRNA are being increasingly implicated in AD. Overall, a complex mesh of deregulated and multi-tasking ncRNAs reciprocally interacts with core pathophysiological mechanisms underlying AD. Alterations in ncRNAs can be detected in CSF and the circulation as well as the brain and are showing promise as biomarkers, with the ultimate goal clinical exploitation as targets for novel modes of symptomatic and course-altering therapy.

Downregulation of Mfn2 participates in manganese-induced neuronal apoptosis in rat striatum and PC12 cells

Manganese (Mn) is a widely distributed trace element that is essential for normal brain function and development. However, chronic exposure to excessive Mn has been known to lead to neuronal loss and manganism, a disease with debilitating motor and cognitive deficits, whose clinical syndrome resembling idiopathic Parkinson's disease (IPD). However, the precise molecular mechanism underlying Mn neurotoxicity remains largely unclear. Accumulating evidence indicates that abnormal mitochondrial functionality is an early and causal event in Mn-induced neurodegeneration and apoptosis. Here, we investigated whether Mitofusin 2 (Mfn2), a highly conserved dynamin-related protein (DRP), played a role in the regulation of Mn-induced neuronal apoptosis. We revealed that Mfn2 was significantly dysregulated in rat striatum and PC12 neuronal-like cells following Mn exposure. Western blot analysis revealed that the expression of Mfn2 was remarkably decreased following different concentrations of Mn exposure. Immunohistochemistry analysis confirmed a remarkable downregulation of Mfn2 in rat striatum after Mn exposure. Immunofluorescent staining showed that Mfn2 was expressed predominantly in neurons, and neuronal loss of Mfn2 was associated with the expression of active caspase-3 following Mn exposure. Importantly, overexpression of Mfn2 apparently attenuated Mn-induced neuronal apoptosis. Notably, treatment with caspase-3 inhibitor Ac-DEVD-CH could not rescue Mn-induced downregulation of Mfn2, suggesting that Mn-induced mfn2 occurs prior to neuronal apoptosis. Taken together, these results indicated that down-regulated expression of Mfn2 might contribute to the pathological processes underlying Mn neurotoxicity.

Depletion of Mitofusin-2 Causes Mitochondrial Damage in Cisplatin-Induced Neuropathy

Sensory neuropathy is a relevant side effect of the antineoplastic agent cisplatin. Mitochondrial damage is assumed to play a critical role in cisplatin-induced peripheral neuropathy, but the pathomechanisms underlying cisplatin-induced mitotoxicity and neurodegeneration are incompletely understood. In an animal model of cisplatin-induced neuropathy, we determined in detail the extent and spatial distribution of mitochondrial damage during cisplatin treatment. Changes in the total number of axonal mitochondria during cisplatin treatment were assessed in intercostal nerves from transgenic mice that express cyan fluorescent protein. Further, we explored the impact of cisplatin on the expression of nuclear encoded molecules of mitochondrial fusion and fission, including mitofusin-2 (MFN2), optic atrophy 1 (OPA1), and dynamin-related protein 1 (DRP1). Cisplatin treatment resulted in a loss of total mitochondrial mass in axons and in an abnormal mitochondrial morphology including atypical enlargement, increased vacuolization, and loss of cristae. These changes were observed in distal and proximal nerve segments and were more prominent in axons than in Schwann cells. Transcripts of fusion and fission proteins were reduced in distal nerve segments. Significant reduced expression levels of the fusion protein MFN2 was detected in nerves of cisplatin-exposed animals. In summary, we provide for the first time an evidence that cisplatin alters mitochondrial dynamics in peripheral nerves. Loss of MFN2, previously implicated in the pathogenesis of other neurodegenerative diseases, also contributes to the pathogenesis in cisplatin-induced neuropathy.

Mitochondrial fission and fusion in secondary brain damage after CNS insults

Mitochondria are dynamically active organelles, regulated through fission and fusion events to continuously redistribute them across axons, dendrites, and synapses of neurons to meet bioenergetics requirements and to control various functions, including cell proliferation, calcium buffering, neurotransmission, oxidative stress, and apoptosis. However, following acute or chronic injury to CNS, altered expression and function of proteins that mediate fission and fusion lead to mitochondrial dynamic imbalance. Particularly, if the fission is abnormally increased through pro-fission mediators such as Drp1, mitochondrial function will be impaired and mitochondria will become susceptible to insertion of proapototic proteins. This leads to the formation of mitochondrial transition pore, which eventually triggers apoptosis. Thus, mitochondrial dysfunction is a major promoter of neuronal death and secondary brain damage after an insult. This review discusses the implications of mitochondrial dynamic imbalance in neuronal death after acute and chronic CNS insults.

Neuroprotective Mechanisms Mediated by CDK5 Inhibition

Cyclin-dependent kinase 5 (CDK5) is a proline-directed serine/threonine kinase belonging to the family of cyclin-dependent kinases. In addition to maintaining the neuronal architecture, CDK5 plays an important role in the regulation of synaptic plasticity, neurotransmitter release, neuron migration and neurite outgrowth. Although various reports have shown links between neurodegeneration and deregulation of cyclin-dependent kinases, the specific role of CDK5 inhibition in causing neuroprotection in cases of neuronal insult or in neurodegenerative diseases is not wellunderstood. This article discusses current evidence for the involvement of CDK5 deregulation in neurodegenerative disorders and neurodegeneration associated with stroke through various mechanisms. These include upregulation of cyclin D1 and overactivation of CDK5 mediated neuronal cell death pathways, aberrant hyperphosphorylation of human tau proteins and/or neurofilament proteins, formation of neurofibrillary lesions, excitotoxicity, cytoskeletal disruption, motor neuron death (due to abnormally high levels of CDK5/p25) and colchicine- induced apoptosis in cerebellar granule neurons. A better understanding of the role of CDK5 inhibition in neuroprotective mechanisms will help scientists and researchers to develop selective, safe and efficacious pharmacological inhibitors of CDK5 for therapeutic use against human neurodegenerative disorders, such as Alzheimer's disease, amyotrophic lateral sclerosis and neuronal loss associated with stroke.

Relationship Between β-Amyloid and Mitochondrial Dynamics

Mitochondria as dynamic organelles undergo morphological changes through the processes of fission and fusion which are major factors regulating their functions. A disruption in the balance of mitochondrial dynamics induces functional disorders in mitochondria such as failed energy production and the generation of reactive oxygen species, which are closely related to pathophysiological changes associated with Alzheimer's disease (AD). Recent studies have demonstrated a relationship between abnormalities in mitochondrial dynamics and impaired mitochondrial function, clarifying the effects of morphofunctional aberrations which promote neuronal cell death in AD. Several possible signaling pathways have been suggested for a better understanding of the mechanism behind the key molecules regulating mitochondrial morphologies. However, the exact machinery involved in mitochondrial dynamics still has yet to be elucidated. This paper reviews the current knowledge on signaling mechanisms involved in mitochondrial dynamics and the significance of mitochondrial dynamics in controlling associated functions in neurodegenerative diseases, particularly in AD.

Peroxiredoxin 5 (Prx5) decreases LPS-induced microglial activation through regulation of Ca2+/calcineurin-Drp1-dependent mitochondrial fission

Microglial activation is a hallmark of neurodegenerative diseases. ROS activates microglia by regulating transcription factors to express pro-inflammatory genes and is associated with disruption of Ca²⁺ homeostasis through thiol redox modulation. Recently, we reported that Prx5 can regulate activation of microglia cells by governing ROS. In addition, LPS leads to excessive mitochondrial fission, and regulation of mitochondrial dynamics involved in a pro-inflammatory response is important for the maintenance of microglial activation. However, the precise relationship among these signals and the role of Prx5 in mitochondrial dynamics and microglial activation is still unknown. In this study, we demonstrated that Ca²⁺/calcineurin-dependent de-phosphorylation of Drp1 induces mitochondrial fission and regulates mitochondrial ROS production, which influences the expression of pro-inflammatory mediators in LPS-induced microglia cells. Moreover, it is likely that cytosolic and Nox-derived ROS were upstream of mitochondrial fission and mitochondrial ROS generation in activated microglia cells. Prx5 regulates LPS-induced mitochondrial fission through modulation of Ca²⁺/calcineurin-dependent Drp1 de-phosphorylation by eliminating Nox-derived and cytosolic ROS. Therefore, we suggest that mitochondrial dynamics may be essential for understanding pro-inflammatory responses and that Prx5 may be used as a new therapeutic target to prevent neuroinflammation and neurodegenerative diseases.

MiR-195 dependent roles of mitofusin2 in the mitochondrial dysfunction of hippocampal neurons in SAMP8 mice

Abnormal gene expression, including mRNAs, and microRNAs (miRNA), have been identified in the development of Alzheimer's disease (AD). Although mitofusin2 (mfn2) has been found to be down-regulated in the neurons from hippocampus and cortex in AD patients, little is known about its roles and the regulatory mechanisms in the pathogenesis of AD. This study was performed to investigate the roles of mfn2 protein and its upstream regulatory mechanism in the progression of AD using a senescence accelerated mouse prone-8 (SAMP8) model. The results of quantitative real-time PCR and western blot revealed that mfn2 expression displayed a consistent decrease with aging in the hippocampus of SAMP8 than did age-matched SAMR1 mice. The luciferase activity assay combined with mutational analysis confirmed the binding site of miR-195 to the 3' -untranslated region (3'-UTR) of mfn2 mRNA. Furthermore, miR-195 inhibitor or antigomir induced the higher level expression of mfn2 protein in vitro and in vivo. In addition, exogenous expression of miR-195 decreased the mitochondrial membrane potential (MMP) of the HT-22 cells by targeting mfn2. In conclusion, these results indicated that deregulation of mfn2 might be involved in mitochondrial dysfunction during the progression of AD, and its decreased expression was regulated at least in part by miR-195 in AD mice. The abnormal expression of miR-195 played a potential role in mitochondrial disorder by targeting mfn2 in hippocampus of SAMP8 mice. Therefore, upregulation of mfn2 protein by inhibiting miR-195 might be a potential new therapeutic strategy for treatment of AD.

Aβ-Induced Drp1 phosphorylation through Akt activation promotes excessive mitochondrial fission leading to neuronal apoptosis

Mitochondrial dysfunction is known as one of causative factors in Alzheimer's disease (AD), inducing neuronal cell death. Mitochondria regulate their functions through changing their morphology. The present work was undertaken to investigate whether Amyloid β (Aβ) affects mitochondrial morphology in neuronal cells to induce apoptosis. Aβ treatment induced not only the fragmentation of mitochondria but also neuronal apoptosis in association with an increase in caspase-9 and -3 activity. Calcium influx induced by Aβ up-regulated the activation of Akt through CaMKII resulting in changes to the phosphorylation level of Drp1 in a time-dependent manner. Translocation of Drp1 from the cytosol to mitochondria was blocked by CB-124005 (an Akt inhibitor). Recruitment of Drp1 to mitochondria led to ROS generation and mitochondrial fission, accompanied by dysfunction of mitochondria such as loss of membrane potential and ATP production. ROS generation and mitochondrial dysfunction by Aβ were attenuated when treated with Mdivi-1, a selective Drp1 inhibitor. Furthermore, the sustained Akt activation induced not only the fragmentation of mitochondria but also the activation of mTOR, eventually suppressing autophagy. Inhibition of autophagic clearance of Aβ led to increased ROS levels and aggravating mitochondrial defects, which were blocked by Rapamycin (an mTOR inhibitor). In conclusion, sustained phosphorylation of Akt by Aβ directly activates Drp1 and inhibits autophagy through the mTOR pathway. Together, these changes elicit abundant mitochondrial fragmentation resulting in ROS-mediated neuronal apoptosis.

Alzheimer's Disease: From Mitochondrial Perturbations to Mitochondrial Medicine

Age-related neurodegenerative diseases such as Alzheimer's disease (AD) are distressing conditions causing countless levels of suffering for which treatment is often insufficient or inexistent. Considered to be the most common cause of dementia and an incurable, progressive neurodegenerative disorder, the intricate pathogenic mechanisms of AD continue to be revealed and, consequently, an effective treatment needs to be developed. Among the diverse hypothesis that have been proposed to explain AD pathogenesis, the one concerning mitochondrial dysfunction has raised as one of the most discussed with an actual acceptance in the field. It posits that manipulating mitochondrial function and understanding the deficits that result in mitochondrial injury may help to control and/or limit the development of AD. To achieve such goal, the concept of mitochondrial medicine places itself as a promising gathering of strategies to directly manage the major insidious disturbances of mitochondrial homeostasis as well as attempts to directly or indirectly manage its consequences in the context of AD. The aim of this review is to summarize the evolution that occurred from the establishment of mitochondrial homeostasis perturbation as masterpieces in AD pathogenesis up until the development of mitochondrial medicine. Following a brief glimpse in the past and current hypothesis regarding the triad of aging, mitochondria and AD, this manuscript will address the major mechanisms currently believed to participate in above mentioned events. Both pharmacological and lifestyle interventions will also be reviewed as AD-related mitochondrial therapeutics.

Mitochondria as a target for neuroprotection: implications for Alzheimer´s disease

INTRODUCTION

Alzheimer's disease (AD), the most common form of dementia, is marked by progressive loss of memory and impairment of cognitive ability. Despite decades of intensive research and scientific advances, the intricate pathogenic mechanisms of AD are still not fully understood and, consequently, an effective treatment is yet to be developed. As widely accepted, the alterations of mitochondrial function are actively engaged in a plethora of neurodegenerative diseases, including AD. With growing interest in the mitochondria as a potential target for understanding AD, it has even been hypothesized that deficits in these organelles may be at the heart of the progression of AD itself. Areas covered: The purpose of this review is to summarize relevant studies that suggest a role for mitochondrial (dys)function in AD and to provide a survey on latest developments regarding AD-related mitochondrial therapeutics. Expert commentary: As outlined in a plethora of studies, there is no doubt that mitochondria play a major role in several stages of AD progression. Even though more in-depth studies are needed before pharmaceutical industry can apply such knowledge to human medicine, the continuous advances in AD research field will certainly facilitate and accelerate the development of more effective preventive or therapeutic strategies to fight this devastating disease.

MIRO GTPases in Mitochondrial Transport, Homeostasis and Pathology

The evolutionarily-conserved mitochondrial Rho (MIRO) small GTPase is a Ras superfamily member with three unique features. It has two GTPase domains instead of the one found in other small GTPases, and it also has two EF hand calcium binding domains, which allow Ca²⁺-dependent modulation of its activity and functions. Importantly, it is specifically associated with the mitochondria and via a hydrophobic transmembrane domain, rather than a lipid-based anchor more commonly found in other small GTPases. At the mitochondria, MIRO regulates mitochondrial homeostasis and turnover. In metazoans, MIRO regulates mitochondrial transport and organization at cellular extensions, such as axons, and, in some cases, intercellular transport of the organelle through tunneling nanotubes. Recent findings have revealed a myriad of molecules that are associated with MIRO, particularly the kinesin adaptor Milton/TRAK, mitofusin, PINK1 and Parkin, as well as the endoplasmic reticulum-mitochondria encounter structure (ERMES) complex. The mechanistic aspects of the roles of MIRO and its interactors in mitochondrial homeostasis and transport are gradually being revealed. On the other hand, MIRO is also increasingly associated with neurodegenerative diseases that have roots in mitochondrial dysfunction. In this review, I discuss what is currently known about the cellular physiology and pathophysiology of MIRO functions.

Iron overload triggers mitochondrial fragmentation via calcineurin-sensitive signals in HT-22 hippocampal neuron cells

The accumulation of iron in neurons has been proposed to contribute to the pathology of numerous neurodegenerative diseases, such as Alzheimer's disease and Parkinson's disease. However, insufficient research has been conducted on the precise mechanism underlying iron toxicity in neurons. In this study, we investigated mitochondrial dynamics in hippocampal HT-22 neurons exposed to ferric ammonium citrate (FAC) as a model of iron overload and neurodegeneration. Incubation with 150 μM FAC for 48 h resulted in decreased cell viability and apoptotic death in HT-22 cells. The FAC-induced iron overload triggered mitochondrial fragmentation, which was accompanied by Drp1(Ser637) dephosphorylation. Iron chelation with deferoxamine prevented the FAC-induced mitochondrial fragmentation and apoptotic cell death by inhibiting Drp1(Ser637) dephosphorylation. In addition, a S637D mutation of Drp1, which resulted in a phosphorylation-mimetic form of Drp1 at Ser637, protected against the FAC-induced mitochondrial fragmentation and neuronal apoptosis. FK506 and cyclosporine A, inhibitors of calcineurin activation, determined that calcineurin was associated with the iron-induced changes in mitochondrial morphology and the phosphorylation levels of Drp1. These results indicate that the FAC-induced dephosphorylation of Drp1-dependent mitochondrial fragmentation was rescued by the inhibition of calcineurin activation. Therefore, these findings suggest that calcineurin-mediated phosphorylation of Drp1(Ser637) acts as a key regulator of neuronal cell loss by modulating mitochondrial dynamics in iron-induced toxicity. These results may contribute to the development of novel therapies for treatment of neurodegenerative disorders related to iron toxicity.

The Role of Cdk5 in Alzheimer's Disease

Alzheimer's disease (AD) is known as the most fatal chronic neurodegenerative disease in adults along with progressive loss of memory and other cognitive function disorders. Cyclin-dependent kinase 5 (Cdk5), a unique member of the cyclin-dependent kinases (Cdks), is reported to intimately associate with the process of the pathogenesis of AD. Cdk5 is of vital importance in the development of CNS and neuron movements such as neuronal migration and differentiation, synaptic functions, and memory consolidation. However, when neurons suffer from pathological stimuli, Cdk5 activity becomes hyperactive and causes aberrant hyperphosphorylation of various substrates of Cdk5 like amyloid precursor protein (APP), tau and neurofilament, resulting in neurodegenerative diseases like AD. Deregulation of Cdk5 contributes to an array of pathological events in AD, ranging from formation of senile plaques and neurofibrillary tangles, synaptic damage, mitochondrial dysfunction to cell cycle reactivation as well as neuronal cell apoptosis. More importantly, an inhibition of Cdk5 activity with inhibitors such as RNA inference (RNAi) could protect from memory decline and neuronal cell loss through suppressing β-amyloid (Aβ)-induced neurotoxicity and tauopathies. This review will briefly describe the above-mentioned possible roles of Cdk5 in the physiological and pathological mechanisms of AD, further discussing recent advances and challenges in Cdk5 as a therapeutic target.

Mitochondrial Dysfunction Contributes to the Pathogenesis of Alzheimer's Disease

Alzheimer's disease (AD) is a neurodegenerative disease that affects millions of people worldwide. Currently, there is no effective treatment for AD, which indicates the necessity to understand the pathogenic mechanism of this disorder. Extracellular aggregates of amyloid precursor protein (APP), called Aβ peptide and neurofibrillary tangles (NFTs), formed by tau protein in the hyperphosphorylated form are considered the hallmarks of AD. Accumulative evidence suggests that tau pathology and Aβ affect neuronal cells compromising energy supply, antioxidant response, and synaptic activity. In this context, it has been showed that mitochondrial function could be affected by the presence of tau pathology and Aβ in AD. Mitochondria are essential for brain cells function and the improvement of mitochondrial activity contributes to preventing neurodegeneration. Several reports have suggested that mitochondria could be affected in terms of morphology, bioenergetics, and transport in AD. These defects affect mitochondrial health, which later will contribute to the pathogenesis of AD. In this review, we will discuss evidence that supports the importance of mitochondrial injury in the pathogenesis of AD and how studying these mechanisms could lead us to suggest new targets for diagnostic and therapeutic intervention against neurodegeneration.

Neuronal stress signaling and eIF2α phosphorylation as molecular links between Alzheimer's disease and diabetes

Mounting evidence from clinical, epidemiological, neuropathology and preclinical studies indicates that mechanisms similar to those leading to peripheral metabolic deregulation in metabolic disorders, such as diabetes and obesity, take place in the brains of Alzheimer's disease (AD) patients. These include pro-inflammatory mechanisms, brain metabolic stress and neuronal insulin resistance. From a molecular and cellular perspective, recent progress has been made in unveiling novel pathways that act in an orchestrated way to cause neuronal damage and cognitive decline in AD. These pathways converge to the activation of neuronal stress-related protein kinases and excessive phosphorylation of eukaryotic translation initiation factor 2α (eIF2α-P), which plays a key role in control of protein translation, culminating in synapse dysfunction and memory loss. eIF2α-P signaling thus links multiple neuronal stress pathways to impaired neuronal function and neurodegeneration. Here, we present a critical analysis of recently discovered molecular mechanisms underlying impaired brain insulin signaling and metabolic stress, with emphasis on the role of stress kinase/eIF2α-P signaling as a hub that promotes brain and behavioral impairments in AD. Because very similar mechanisms appear to operate in peripheral metabolic deregulation in T2D and in brain defects in AD, we discuss the concept that targeting defective brain insulin signaling and neuronal stress mechanisms with anti-diabetes agents may be an attractive approach to fight memory decline in AD. We conclude by raising core questions that remain to be addressed toward the development of much needed therapeutic approaches for AD.

Extrinsic plasmalogens suppress neuronal apoptosis in mouse neuroblastoma Neuro-2A cells: importance of plasmalogen molecular species

Plasmalogen, especially those having 22:6, suppressed neuronal apoptosisviadeath receptor and mitochondrial pathways. These mechanisms of action of plasmalogen may be responsible for regulation of membrane functions and second messenger production.